thematic vs thematical

thematic

adj
  • Relating to, or having a theme (“subject”) or a topic. 

  • Relating to a melodic subject. 

  • Of or relating to a theme (“subdivision of the Byzantine empire”). 

  • Of a word stem, ending in a vowel that appears in or otherwise influences the noun or verb's inflection. 

noun
  • A postage stamp that is part of a thematic collection. 

thematical

adj
  • thematic 

How often have the words thematic and thematical occurred in a corpus of books? (source: Google Ngram Viewer )